Joan Herbers' favourites

Joan Herbers is a population biologist at Ohio State University. Her research program has focused on the ecology, genetics, and evolution of social structure in insects, with particular emphasis on ant colonies.

"Biology Letters contains first-rate articles, and many have what we Americans call the 'gee whiz' factor. I chose three such papers that caught my eye in the past few months. Nature is truly stranger than fiction. 'Gee whiz' stories provoke the imagination, force us to reinterpret old data, and most importantly, stimulate multiple lines of additional research. I hope you enjoyed some of these recent reports as much as I did."

"I recently visited the Shedd Aquarium in Chicago, and observed hordes of kids clustered around a tank. The fish in that tank weren't doing anything in particular, at least not to my eye. As I edged closer and peered over little heads, I heard static sounds from a loudspeaker - aha, these were electric fish!
The report by Feulner et al. focuses on fish that emit weak electric signals; these animals live in the Congo river, and the three species studied here differ in the spectra of electric signals emitted. Although males and females within a species do not differ, the authors nonetheless wondered if the species-specificity of the signals might provide insight to mating biology. They recorded signals from multiple individuals of the three species, and statistical analysis confirmed discrete species differences in the discharges. They then used females of one species as focal individuals to test for affiliative behavior. In choice tests. females strongly preferred conspecific males, and the extent of the preference had phylogenetic signal as well."

Abstract
Mate choice is mediated by a range of sensory cues, and assortative mating based on these cues can drive reproductive isolation among diverging populations. A specific feature of mormyrid fish, the electric organ discharge (EOD), is used for electrolocation and intraspecific communication. We hypothesized that the EOD also facilitates assortative mating and ultimately promotes prezygotic reproductive isolation in African weakly electric fishes. Our behavioural experiments using live males as well as EOD playback demonstrated that female mate recognition is influenced by EOD signals and that females are attracted to EOD characteristics of conspecific males. The dual function of the EOD for both foraging and social communication (including mate recognition leading to assortative mating) underlines the importance of electric signal differentiation for the divergence of African weakly electric fishes. Thus, the EOD provides an intriguing mechanism promoting trophic divergence and reproductive isolation between two closely related Campylomormyrus species occurring in sympatry in the lower Congo rapids.

Raising the sauropod neck: it costs more to get less.

"Remember the scene in Jurassic Park where the kids wake up high in a tree to find a large dinosaur munching on tree leaves nearby? Well, that scene needs to be re-written, and museum displays also should reposition the necks on some of their dinosaur displays. Seymour reviews several articles on the physics of blood circulation, and adds some new analysis to show that if Apatosaurus really did raise its head to chomp on high vegetation, it had to pay a high metabolic price. Given a neck length of 9 meters, a large sauropod would require a gigantic heart to pump blood up to the head, and half its cardiac output would be devoted to that task alone. Furthermore, the basal metabolic rate required to support that kind of circulation would need to be nearly twice that required if the animal simply kept its head down.

Seymour argues that the metabolic costs of feeding high in vegetation simply were not supportable, especially given that there was plenty to eat lower down. I was certainly convinced that these large dinosaurs had to keep a low profile to avoid passing out!"

Abstract
The long necks of gigantic sauropod dinosaurs are commonly assumed to have been used for high browsing to obtain enough food. However, this analysis questions whether such a posture was reasonable from the standpoint of energetics. The energy cost of circulating the blood can be estimated accurately from two physiological axioms that relate metabolic rate, blood flow rate and arterial blood pressure: (i) metabolic rate is proportional to blood flow rate and (ii) cardiac work rate is proportional to the product of blood flow rate and blood pressure. The analysis shows that it would have required the animal to expend approximately half of its energy intake just to circulate the blood, primarily because a vertical neck would have required a high systemic arterial blood pressure. It is therefore energetically more feasible to have used a more or less horizontal neck to enable wide browsing while keeping blood pressure low.

"Pitcher plants live in nutrient-poor environments and most acquire the nitrogen they need by trapping insects. Any field trip to a bog or marsh will involve a hunt for these charismatic plants. The article here shows that in southeast Asia a species has invented yet another way to secure nitrogen: offer nectar resources to tree shrews.

This species has two morphs of pitchers; on young individuals, only the standard kind of pitcher is produced. Like other pitcher plants, the juveniles have specialized glands that attract insects, and a slippery surface that causes them to fall into the water below and drown. The pitchers then dissolve their insect prey, just like all their relatives. On older plants, though, the need for nitrogen is elevated. These plants have a second kind of pitcher with distinctly different morphology. The robust funnel-shaped pitchers have enlarged mouths and nectar glands that secrete a buttery exudate; they also have a rough inner surface and hence do not accumulate insect carcases. Rather, tree shrews visit these pitchers to feed on the exudate; when a shrew perches on the pitcher's mouth to feed, it often defecates into the pitcher. Clarke et al show that shrew feces are rich in nitrogen and in fact represent these pitchers' major source of that essential nutrient."

AbstractNepenthes pitcher plants are typically carnivorous, producing pitchers with varying combinations of epicuticular wax crystals, viscoelastic fluids and slippery peristomes to trap arthropod prey, especially ants. However, ant densities are low in tropical montane habitats, thereby limiting the potential benefits of the carnivorous syndrome. Nepenthes lowii, a montane species from Borneo, produces two types of pitchers that differ greatly in form and function. Pitchers produced by immature plants conform to the 'typical' Nepenthes pattern, catching arthropod prey. However, pitchers produced by mature N. lowii plants lack the features associated with carnivory and are instead visited by tree shrews, which defaecate into them after feeding on exudates that accumulate on the pitcher lid. We tested the hypothesis that tree shrew faeces represent a significant nitrogen (N) source for N. lowii, finding that it accounts for between 57 and 100 per cent of foliar N in mature N. lowii plants. Thus, N. lowii employs a diversified N sequestration strategy, gaining access to a N source that is not available to sympatric congeners. The interaction between N. lowii and tree shrews appears to be a mutualism based on the exchange of food sources that are scarce in their montane habitat.